In general, mixing machines are fairly well known. However, given the temperature specifics of the injection molding process and the mixing properties of plasticizable compounds, mixing machines for use in combination with extrusion or injection molding are fairly narrowly defined. U.S. Pat. No. 5, 267,788 teaches a multi-screw continuous mixing and kneading machine with polygonal kneading elements for plasticizable compounds. The multi-screw machine rotates within a housing and encloses the screws which are polygonal in design. However, given the large diameter of the mixing screws and the small volume for flow of the compounds, this design requires an exceedingly high pressure force to turn the mixer. Additionally, this patent is directed particularly at preventing premature melting of the plasticizable compounds and reducing the shear force within the mixing chamber.
Other mixing type machines are also known to mix various plasticizable compounds. These designs include a drive type shaft rotating within a housing and having cylindrical mixing members extending outwardly therefrom. These cylindrical members are utilized to agitate and mix both the base and color material before depositing the compounds into the molding machines.
The problem with the above referenced prior art mixers is that adequate and thorough mixing of the two compounds must be completed prior to depositing the compounds into the molding machine. Otherwise, the material utilized in the molding machines may be only slightly colored or possibly even discolored based upon inadequate mixing. This discoloration may be seen in the form of streaking or a mottled appearance in the final molded product. Additionally, due to the construction of these mixers, cleaning and disassembly is a fairly difficult task. The mixer design of the present invention seeks to overcome these shortcomings.